Here are my favorite lines:
"There is no pretending," Jace said with absolute clarity. "I love you, and I will love you until I die, and if there is life after that, I'll love you then.”

“And now I’m looking at you,” he said, “and you’re asking me if I still want you, as if I could stop loving you. As if I would want to give up the thing that makes me stronger than anything else ever has. I never dared give much of myself to anyone before – bits of myself to the Lightwoods, to Isabelle and Alec, but it took years to do it – but, Clary, since the first time I saw you, I have belonged to you completely. I still do. If you want me.”

“Not everything is about you," Clary said furiously.
"Possibly," Jace said, "but you do have to admit that the majority of things are.”